Naturphilosophie (German for "nature-philosophy") is a term used in English-language philosophy to identify a current in the philosophical tradition of German idealism, as applied to the study of nature in the earlier 19th century. German speakers use the clearer term Romantische Naturphilosophie, the philosophy of nature developed at the time of the founding of German Romanticism. It is particularly associated with the philosophical work of Friedrich Wilhelm Joseph von Schelling and Georg Wilhelm Friedrich Hegel—though it has some clear precursors also. More particularly it is identified with some of the initial works of Schelling during the period 1797–9, in reaction to the views of Fichte, and subsequent developments from Schelling's position. Always controversial, some of Schelling's ideas in this direction are still considered of philosophical interest, even if the subsequent development of experimental natural science had a destructive impact on the credibility of the theories of his followers in Naturphilosophie.

Naturphilosophie attempted to comprehend nature in its totality and to outline its general theoretical structure, thus attempting to lay the foundations for the natural sciences. In developing their theories, the German Naturphilosophen found their inspiration in the natural philosophy of the Ancient Greek Ionian philosophers.

As an approach to philosophy and science, Naturphilosophie has had a difficult reception. In Germany, neo-Kantians came to distrust its developments as speculative and overly metaphysical. For most of the 19th and early 20th centuries, it was poorly understood in Anglophone countries. Over the years, it has been subjected to continuing criticism. Since the 1960s, improved translations have appeared, and scholars have developed a better appreciation of the objectives of Naturphilosophie.